From: Heiko Schlittermann (HS12-RIPE) <hs@schlittermann.de>
Date: Mon, 5 Feb 2018 21:23:32 +0000 (+0100)
Subject: Fix base64d() buffer size (CVE-2018-6789)
X-Git-Tag: exim-4_91_RC1~61
X-Git-Url: https://git.exim.org/users/heiko/exim.git/commitdiff_plain/cf3cd306062a08969c41a1cdd32c6855f1abecf1?ds=inline

Fix base64d() buffer size (CVE-2018-6789)

Credits for discovering this bug: Meh Chang <meh@devco.re>

(cherry picked from commit 062990cc1b2f9e5d82a413b53c8f0569075de700)
---

diff --git a/doc/doc-txt/ChangeLog b/doc/doc-txt/ChangeLog
index 1ee00168f..8ae418ab1 100644
--- a/doc/doc-txt/ChangeLog
+++ b/doc/doc-txt/ChangeLog
@@ -5,8 +5,8 @@ affect Exim's operation, with an unchanged configuration file.  For new
 options, and new features, see the NewStuff file next to this ChangeLog.
 
 
-Exim version 4.91
------------------
+Since Exim version 4.90
+-----------------------
 
 JH/01 Replace the store_release() internal interface with store_newblock(),
       which internalises the check required to safely use the old one, plus
@@ -82,6 +82,8 @@ JH/15 Relax results from ACL control request to enable cutthrough, in
       ignoring.  This covers use with PRDR, frozen messages, queue-only and
       fake-reject.
 
+HS/01 Fix Buffer overflow in base64d() (CVE-2018-6789)
+
 JH/16 Fix bug in DKIM verify: a buffer overflow could corrupt the malloc
       metadata, resulting in a crash in free().
 
diff --git a/src/src/base64.c b/src/src/base64.c
index ae6874b8a..1d84c1e5c 100644
--- a/src/src/base64.c
+++ b/src/src/base64.c
@@ -152,10 +152,14 @@ static uschar dec64table[] = {
 int
 b64decode(const uschar *code, uschar **ptr)
 {
+
 int x, y;
-uschar *result = store_get(3*(Ustrlen(code)/4) + 1);
+uschar *result;
 
-*ptr = result;
+{
+  int l = Ustrlen(code);
+  *ptr = result = store_get(1 + l/4 * 3 + l%4);
+}
 
 /* Each cycle of the loop handles a quantum of 4 input bytes. For the last
 quantum this may decode to 1, 2, or 3 output bytes. */